1. Field of the Invention
The present invention relates to a relay device, a relay method and a relay program, which are used in a communication network, wherein the network carries out both real-time communications and non-real-time communications. The present invention may be used for a broadband router compatible with, for example, both Internet-connection services, and Internet-protocol (IP) telephone services.
2. Description of Related Art
For example, the Internet and a local area network (LAN) have been known as a communication network which carries out both real-time communications and non-real-time communications. In the above communication networks, both the real-time communications and the non-real-time communications are carried out using a same transmission band.
The real-time communication is the communication in which allowable delay time is defined. For example, an IP telephone system, a video telephone system, a facsimile system, and a television conference system have been known as the real-time communications.
The non-real-time communication is the communication in which there is no limit in the delay time. Data communications such as the World Wide Web (WWW), and File-Transfer-Protocol (FTP) Transfer have been known as the non-real-time communications.
For example, a broadband router has been known as a relay device used in a communication network compatible with real-time communications and non-real-time communications. FIG. 1 shows a conceptual view showing one example of a communication network using a broadband router. A communication network 110 in FIG. 1 includes a broadband router 111, LAN terminals 112 through 114, and an IP telephone 115. The broadband router 111 has communication functions for a wide area network (WAN), a LAN, a wireless LAN, and a Voice over IP (Vol P) technology. The broadband router 111 is connected to the Internet 120 through a WAN. Furthermore, the broadband router 111 accommodates terminals 112 and 113 through LAN cables, a terminal 114 using wireless communications, and a telephone 115 through analog cables. In the example of FIG. 1, the terminals 112 through 114 carry out non-real-time communications, and, moreover, the IP telephone 115 carries out real-time communications.
When real-time communications and non-real-time communications are carried out using a same transmission band, a technique is necessary for preventing delay time in the real-time communications from exceeding an allowed value. The reason is that, when the delay time in the real-time communications exceeds the allowed value, there is a possibility that overflow of communication data is generated in a buffer of a relay device. The overflow of communication data causes delay in data transfer and loss of data. Accordingly, communication quality is deteriorated.
A communication device which can inhibit overflow in real-time communications has been disclosed in Japanese Patent Application Laid-Open No. 2004-208124. The communication device according to the above-described patent document is provided with a function by which a data amount in real-time communications is monitored. The communication device extends a transmission bandwidth allocated for real-time communications when the data amount in the real-time communications exceeds a predetermined threshold.
However, when the data amount in the real-time communications is rapidly changed, it is difficult to prevent overflow of communication data because the communication device according to the above-described patent document changes the allocated transmission bandwidth after the data amount actually exceeds the threshold. Accordingly, it seems that the overflow is easily generated in the above-described communication device immediately after the real-time communications are started.
In the communication device according to the above-described patent document, only a data amount in real-time communications is monitored, and a data amount in non-real-time communications is not monitored. Accordingly, deterioration in communication quality at real-time communications cannot be prevented in the above-described communication device, wherein the deterioration is caused by a large amount of data in the non-real-time communications and by burst-like increase in a data amount at the non-real-time communications.
In order to reduce the cost of a relay device, it is preferable to use a low-price central processing unit (CPU) for the relay device. Especially, a consumer-use broadband router is strongly required to be a low-price one. Use of a low-price CPU requires reduction in the load on communication processing. When real-time communications and non-real-time communications are carried out using one relay device, the processing load on non-real-time communications is large to cause a possibility that communication quality in real-time communications is deteriorated.